Magnetic nanocomposite based on montmorillonite, Fe oxides, and hydrothermal carbon: Synthesis, characterization and pollutants adsorption tests

Abstract

This work presents the synthesis and characterization of montmorillonite-Fe oxides (Mt-Mag) and Mt-Fe oxides-carbon (Mt-Mag-C) systems as adsorbent materials, prepared by efficient and low-cost procedures. Fe oxides were synthesized by alkaline oxidation in the presence of nitrates while carbonization was hydrothermally synthesized. The adsorption capacity of the synthesized materials was tested against different pollutants (norfloxacin, thiabendazole, thiophanate-methyl, oxytetracycline, P4R and Cr(VI)). Fe particles and carbon were not homogeneously distributed while Mt-Mag-C sample presented a lower specific surface area and porosity than Mt-Mag, related to carbon presence, while magnetic nanoparticles seem not to block Mt external pores. Both materials revealed negative surface charge, indicating that is dominated by montmorillonite. Besides, Mt structure seems to be modified by both Fe oxides and carbon synthesis. The magnetic response was higher in Mt-Mag-C than in Mt-Mag, indicating Fe phases modifications during carbonization. The principal identified Fe oxide was magnetite, with minor contributions of paramagnetic Fe3+, goethite, and paramagnetic relaxation, with a significantly increased of the spectral area of the latter in Mt-Mag-C. Fe concentration determined by Mössbauer spectroscopy resulted higher on Mt-Mag-C than Mt-Mag, indicating that Fe atoms located at the interlayer space of montmorillonite, that give not Mössbauer signal, are exposed by sonication and carbon synthesis, and new magnetite particles are formed through the reduction of Fe3+ atoms in dextrose aqueous solution. The paramagnetic relaxation increase is related to new magnetite particles, that, because of carbon presence, cannot be magnetically coupled. A significant sorption capacity was found for cationic and zwitterionic compounds, revealing the relevance of electrostatic interaction. The magnetic response of Mt-Mag-C and the results of sorption tests for cationic and zwitterionic compounds, claims Mt-Mag-C as a promising sorbent material.